1. Field of the Invention
The present application relates to a compressed natural gas injector which provides armature needle dampening during closing of the fuel valve.
2. Description of the Related Art
Compressed natural gas (hereinafter sometimes referred to as xe2x80x9cCNGxe2x80x9d) is becoming a common automotive fuel for commercial fleet vehicles and residential customers. In vehicles, the CNG is delivered to the engine in precise amounts through gas injectors, hereinafter referred to as xe2x80x9cCNG injectorsxe2x80x9d. The CNG injector is required to deliver a precise amount of fuel per injection pulse and maintain this accuracy over the life of the injector. In order to maintain this level of performance for a CNG injector, certain strategies are required to help reduce the effects of contaminants in the fuel.
Compressed natural gas is delivered throughout the country in a pipeline system and is mainly used for commercial and residential heating. While the heating systems can tolerate varying levels of quality and contaminants in the CNG, the tolerance levels in automotive gas injectors is significantly lower.
These contaminants, which have been acceptable for many years in CNG used for heating, affect the performance of the injectors to varying levels and will need to be considered in future CNG injector designs. Some of the contaminants found in CNG are small solid particles, water, and compressor oil. Each of these contaminants needs to be addressed in the injector design for the performance to be maintained over the life of the injector.
The contaminants can enter the pipeline from several sources. Repair, maintenance and new construction to the pipeline system can introduce many foreign particles into the fuel. Water, dust, humidity and dirt can be introduced in small quantities with ease during any of these operations. Oxides of many of the metal types found in the pipeline can also be introduced into the system. In addition, faulty compressors can introduce vaporized compressor oils which blow by the seals of the compressor and enter into the gas. Even refueling can force contaminants on either of the refueling fittings into the storage cylinder. Many of these contaminants are likely to reach vital fuel system components and alter the performance characteristics over the life of the vehicle.
In general, fuel injectors require extremely tight tolerances on many of the internal components to accurately meter the fuel. For CNG injectors to remain contaminant tolerant, the guide and impact surfaces for the armature needle assembly require certain specifically unique characteristics.
In addition to fuel contamination problems using CNG, the fuel injectors inherently present additional problems. For example, the problems inherent to dampening or lack of dampening of the needle/armature assembly upon closing as well as upon opening of the fuel valve are unique to fuel injectors utilizing CNG.
The CNG injector is required to open and close very quickly. This quick closing creates a relatively severe impact between the armature and the seat. In the CNG injector, the factors which affect impact velocity between the armature and inlet connector are more severe than in a gasoline injector. The CNG injector has high lift, and lower viscosity (CNG) fluid when compared with a gasoline injector.
A CNG injector requires much higher flow area to get the same amount of energy flow through the injector during a given pulse. This is caused by the lower density of the gaseous CNG when compared to standard liquid fuels such as gasoline. This requires that the lift for a CNG injector valve needle be greater than that of a standard gasoline injector.
The increased lift creates two problems. First, the increased lift increases the amount of energy stored in the spring. This high potential energy stored in the spring is required to allow the injector to operate consistently as the viscosity of the fuel changes. Second, the velocity reached during the longer flight times can be high, creating higher impact forces. We have invented a fuel injector which incorporates a flow restricting orifice device which assists in dampening of the armature/needle assembly upon closing in a manner which improves performance of the engine, particularly when utilized in a fuel injector having several fuel flow paths therethrough, a feature which avoids the problems inherent with contaminated compressed natural gaseous fuels.
An electromagnetically operable fuel injector for a gaseous fuel injection system of an internal combustion engine is disclosed, the injector having a generally longitudinal axis, which comprises a ferromagnetic core, a magnetic coil at least partially surrounding the ferromagnetic core, and an armature magnetically coupled to the magnetic coil and being movably responsive to the magnetic coil. The armature actuates a valve closing element which interacts with a fixed valve seat of a fuel valve and is movable away from the fixed valve seat when the magnetic coil is excited. The fixed valve seat defines an aperture of predetermined dimension for passage of fuel therethrough. The armature has a generally elongated shape and a generally central opening for axial reception and passage of gaseous fuel from a fuel inlet connector positioned adjacent thereto. The fuel inlet connector and the armature are adapted to permit a first flow path of gaseous fuel between the armature and the magnetic coil as part of a path leading to the fuel valve. An orifice device is positioned downstream of the fuel valve and defines an orifice for reception of fuel from the fuel valve, the orifice being of lesser dimension than the aperture of the fixed valve seat.
In a preferred embodiment, an electromagnetically operable fuel injector for a compressed natural gas fuel injection system of an internal combustion engine is disclosed, the injector having a generally longitudinal axis, which comprises a ferromagnetic core, a magnetic coil at least partially surrounding the ferromagnetic core, and an armature coupled to the magnetic coil and movably responsive to the magnetic coil, the armature having a first upper end face and a lower end portion. A valve closing element is connected to the lower end portion of the armature and is interactive with a fixed valve seat which defines a fuel passage aperture to selectively permit fuel to pass through the aperture as the valve closing element is moved to a valve open position by the armature. An orifice device is positioned adjacent and downstream of the fuel valve, the orifice device having an orifice in general alignment with the fuel passage aperture and being dimensioned less than the aperture to restrict the flow of fuel from the fuel valve to thereby provide dampening of the valve closing element upon closing. A fuel inlet connector extends in a generally longitudinal direction above the armature and defines a path for fuel to enter the fuel inlet connector to be directed toward the armature, the fuel inlet connector having a lowermost end portion having a lowermost surface spaced above the armature to define a working gap through which the armature is movable. The armature has a fuel reception portion for receiving fuel directed from the fuel inlet connector. The armature further defines a generally axial fuel passage and at least a first fuel flow aperture extending through a wall portion thereof for directing fuel from the fuel inlet connector through the generally axial fuel passage and into the aperture toward the fixed valve seat for entry into an air intake manifold for the engine. The fuel flow aperture is oriented generally transverse to the longitudinal axis.
A method of directing gaseous fuel through an electromagnetically operable fuel injector for a fuel system of an internal combustion engine is also disclosed, the injector having a generally longitudinal axis, and including a fuel inlet end portion and a fuel outlet end portion, a fuel inlet connector positioned at the fuel inlet end portion and having a fuel inlet end portion. An armature is positioned adjacent the fuel outlet end portion of the fuel inlet connector, the armature being spaced from the fuel inlet connector to define a working gap to permit movement of the armature toward and away from the fuel inlet connector to selectively open and close a fuel valve by providing upward and downward movement of a valve closing element to selectively permit gaseous fuel to pass therethrough to an air intake manifold. The method comprises directing the gaseous fuel to pass axially through the fuel inlet connector, directing the gaseous fuel to pass from the fuel inlet connector to the generally elongated central opening of the armature in an axial direction toward the fuel valve, and restricting the passage of fuel exiting from the fuel valve so as to provide dampening of the valve closing element upon closing of the fuel.